1. Field of Invention
The present invention relates to an active matrix liquid crystal display device using a thin film transistor and its manufacturing method.
2. Description of Related Art
From the past, there have been known active matrix liquid crystal display devices and liquid crystal panels of a structure having interposed twisted nematic (TN) liquid crystal or ferroelectric liquid crystal, used as an optically modulated material, between a thin film transistor substrate and an opposing substrate. In these liquid crystal display devices, a thin film transistor (TFT) and a pixel electrode selectively driven by the TFT are provided on a thin film-transistor substrate, and the opposing electrode is provided on the opposing substrate.
FIG. 1 shows one example of a conventional liquid crystal display device. The size of the thin film transistor in the drawings is shown larger than its actual size in order to clearly represent the structure of the thin film transistor. Liquid crystal 103 is interposed between thin film transistor substrate 101 and opposing substrate 102. Opposing substrate 102 are formed a black matrix 104 composed of a light-blocking film such as chrome, and red, green, and blue color filter sections 105, 106, 107 formed by gelatin dyed with red, green, and blue color. On these are formed a protective insulation film 108 and an opposing electrode 109 composed of a transparent conductive film. Meanwhile, on the inside of thin film transistor substrate 101 are formed a thin film transistor 115 constituted by a gate insulation film 110, gate line 111, source line 112, interlevel insulator film 113, and contact hole 114, and a selectively driven pixel electrode 116 composed of a transparent conductive film. Alignment films 117 and 118 are formed on pixel electrode 116 and opposing electrode 109, and they are applied with rubbing processing. On source line 112 is formed an insulation film 119 composed of a protective film, and this insulation film is removed on the top of pixel electrode 116, opening a window. Thus, source line 112 can be protected. In addition, the insulation film helps prevent the reduction of voltage applied to the liquid crystal. The distance between pixel electrode and opposing electrode is generally called a cell gap, and it is a parameter that greatly controls the optical properties. This cell gap deviates more easily as the liquid crystal panel becomes larger. Therefore, uniformity is maintained in a large liquid crystal panel by using a gap member (spacer) 120.
However, there are four major problems in the above-mentioned previous technology, as described below.
First, when matching a thin film transistor and an opposing substrate, it is necessary to take a large margin for alignment of the pixel electrodes formed on the thin film transistor and the color filters and black matrix formed on the opposing substrate. This greatly reduces the aperture size. It is understood that this problem can be improved somewhat by forming the black matrix on the thin film transistor substrate, and various companies are conducting examinations. For example, in Japanese Laid-Open Patent No. 2-207222, a method is disclosed whereby a light-blocking film for becoming a black matrix is formed on a thin film transistor substrate.
When forming a black matrix on the side of the thin film transistor substrate, a resist having a light-blocking material added, such as black resist is considered to be the most superior material to compose the black matrix. However, use of a resist presents three further problems.
Problem 1-1 is possible contamination from Na, and the like. There are known black resists having mixed red, green, and blue dyes, but these resists contain a large quantity of impurities. Thus, there is a concern of degradation of thin film transistor properties due to Na contamination.
Problem 1-2 is alignment defects. The relationship between film thickness and the light-shielding property in a black resist such as that mentioned above is shown in FIG. 2. In order to obtain a more sufficient light-blocking property (light transmissivity less than or equal to 1.5%, OD value greater than or equal to 1.8), it is clear that at least a film thickness 1.5 xcexcm or more becomes necessary. In this case, rubbing can no longer be performed well due to the difference of levels, and alignment defects of the liquid crystal are caused following the pattern of the black matrix.
On the other hand, specific resistance is also important. When trying to form a pattern so as to cross the space between pixel electrodes, it is required that the specific resistance be sufficiently high in relation to the liquid crystal. Also, the light-blocking property and specific resistance are reciprocal, and establishing both of them is difficult. The specific resistance in the above-mentioned black resist depends also on the film thickness, but it is about 108 xcexa9cm, and it does not meet the specification.
Alignment defects may also be caused by the processed shape of the black resist. An example of that is shown in FIG. 3. The black resist has an overhang structure, and the part under the overhang (point A of FIG. 3) is in a location where rubbing is difficult to perform.
Problem 1-3 is the increase of number of processes. Even the number of masks necessarily on the thin film transistor substrate increases by one sheet.
The second major problem of the previous technology is the degradation of properties of a thin film transistor due to ultraviolet light. FIG. 4 is a comparison of the properties of a thin film transistor before and after ultraviolet irradiation. It is clear that the properties are degraded due to irradiation by ultraviolet radiation as shown in FIG. 4. Ultraviolet-hardened adhesives are used widely when matching a thin film transistor substrate and an opposing substrate. Also, because the thin film transistors are also exposed to ultraviolet radiation during actual use, ultraviolet radiation has become a great obstacle against assuring reliability of thin film transistors.
The third major problem is the use of spacers. If the process of scattering spacers can be omitted, an increase in throughput and a reduction of cost can be realized.
The fourth major problem is the etching of anti-static wiring. Although it was not explained in the above-mentioned previous technology, in order to protect yield from static electricity when forming a thin film transistor substrate, a method is used whereby the gate line patterns are first shorted, and then separated. Nevertheless, this is creates an undesired increase in the number of processes.
The present invention provides an approach to solve the technical problems described above by making it possible to form a black matrix on the side of a thin film transistor substrate without increasing the number of processes or creating alignment defects. Similarly, it becomes possible to perform etching of anti-static wiring without increasing the number of processes. Furthermore, degradation of properties of the thin film transistor due to ultraviolet radiation is prevented, and it becomes possible to omit the process of scattering spacers.
In order to solve the above-mentioned problems, the invention includes a protective film layer formed between the pixel electrode and the black matrix. By this, a low specific resistance of the black matrix no longer causes an influence in image quality.
The invention also includes an ultraviolet light-blocking layer formed on the thin film transistor for preventing the degradation of properties.
The invention also provides the black matrix serving as an ultraviolet light-blocking layer. Consequently, it becomes possible to prevent the increase in the number of processes due to forming an ultraviolet light-blocking layer.
The invention further provides the black matrix serving as a spacer. By this, the process of scattering spacers can be omitted, resulting in an improvement of throughput and reduction of cost.
The invention further provides that the pattern composed of the black matrix and the insulation film formed on its upper layer serve as a spacer.
The invention also provides that the pattern composed of the black matrix and the protective film formed on its lower layer serves as a spacer.
The invention provides a black matrix on the pixel electrode with anti-static wiring formed on its lower part separated using this pattern as a mask. Anti-static wiring is generally provided outside the display area. Meanwhile, a black matrix is for blocking light in the perimeter of the pixel electrodes. Consequently, even when the pattern of a black matrix is formed for the purpose of separating the anti-static wiring, it does not cause a bad influence in the display properties. By this invention, it has become possible to reduce the number of processes and the cost.
The invention also provides a pattern of protective film formed on the pixel electrode, and anti-static wiring formed on the lower part that is separated using this pattern as a mask. Anti-static wiring is generally provided outside the display area. Meanwhile, the pattern of a protective film is for opening windows on the pixel electrodes. Consequently, even when the pattern of a protective film is formed for the purpose of separating the anti-static wiring, it does not cause a bad influence in the display properties. Therefore, by this invention, it is possible to reduce the number of processes and the cost.
The invention further provides a protective film layer formed on the pixel electrode, a black matrix further provided on an upper layer of the liquid crystal display device, the protective film layer etched to be self-aligning in relation to the pattern of said black matrix, and anti-static wiring formed on the lower part separated using this pattern as a mask. Anti-static wiring is generally provided outside the display area. Meanwhile, the patterns of a black matrix and a protective film are for blocking light in the perimeter of the pixel electrodes and for opening windows on the pixel electrodes. Consequently, even when the pattern of a black matrix is formed for the purpose of separating the anti-static wiring, it does not cause a bad influence in the display properties. By this invention, it has become possible to reduce the number of processes and the cost.
The invention also provides anti-static wiring partially exposed when opening a contact hole for connecting a source line or pixel electrode. The anti-static wiring is separated using the pattern of the black matrix provided on the pixel electrode as a mask. Anti-static wiring is commonly performed with gate lines, but in addition to this, an interlevel insulator film is formed. Consequently, before separation, a part of the anti-static wiring should be partially exposed when opening contact holes so that it can be separated without undue trouble. Also, anti-static wiring is generally provided outside the display area. Meanwhile, a black matrix is provided for blocking light in the perimeter of the pixel electrodes. Consequently, even when the pattern of a black matrix is formed for the purpose of separating the anti-static wiring, the protective film does not cause a bad influence in the display properties. By this invention, it has become possible to reduce the number of processes and the cost.
The invention also provides anti-static wiring partially exposed when opening a contact hole for connecting a source line or pixel electrode. Again, the anti-static wiring is separated using the pattern of the protective film provided on the pixel electrode as a mask. Anti-static wiring is commonly performed with gate lines, but in addition to this, an interlevel insulator film is formed. Consequently, before separation, a part of the anti-static wiring should be partially exposed when opening contact holes so that it can be separated without undue trouble. Also, anti-static wiring is generally provided outside the display area. Meanwhile, the pattern of a protective film is provided for opening a window the pixel electrodes. Consequently, even when the pattern of a protective film is formed for the purpose of separating the anti-static wiring, the protective film does not cause a bad influence in the display properties. By this invention, it has become possible to reduce the number of processes and the cost.
The invention also provides anti-static wiring partially exposed when opening a contact hole for connecting a source line or pixel electrode, where the anti-static wiring is separated using the pattern of the protective film provided on the pixel electrode as a mask. Anti-static wiring is commonly performed with gate lines, but in addition to this, an interlevel insulator film is formed. Consequently, before separation, a part of the anti-static wiring should be partially exposed when opening contact holes so that it can be separated without undue trouble. Also, anti-static wiring is generally provided outside the display area. Meanwhile, the patterns of a black matrix and a protective film are provided for blocking light in the perimeter of the pixel electrodes and for opening a window the pixel electrodes. Consequently, even when the pattern of a protective film is formed for the purpose of separating the anti-static wiring, the protective film does not cause a bad influence in the display properties. By this invention, it has become possible to reduce the number of processes and the cost.
It is a further object of the invention to form a protective film layer between the pixel electrodes and the black matrix without any influence on image quality even when the specific resistance of the black matrix is low. Also, Na contamination, and the like, from the dyes, and the like, used for the light-blocking material can be revented.
By etching the protective film layer on the lower part of the liquid crystal display device using the pattern of the black matrix as a mask, one sheet is sufficient for the masks necessary for elimination of the protective film on the pixel electrode section. By this, it becomes possible to maintain a minimum number of processes. Furthermore, by performing etching of the protective film layer by anisotropic etching, rubbing defects caused by the processed shape of the black matrix can also be prevented.
By also forming the pattern of a black matrix also in the seal section, the pattern of the black matrix becomes a part of the protective film of the seal section, and thus improves reliability. Also, even when etching the protective film on the lower layer of the liquid crystal display device with the pattern of the black matrix as a mask, exposing of the wiring can be prevented.
By forming the pattern of the black matrix as a guide when matching the opposing substrate with the thin film transistor substrate, there are no occurrences of irregularities when matching the opposing substrate, even when the black matrix material covers substantially the entirety of the thin film transistor substrate.
By also forming the pattern of a black matrix on the driver section in an active matrix liquid crystal display device having a driver installed inside, the pattern of the black matrix becomes a part of the driver section, thus improving reliability. Also, etching the protective film on the lower layer of the liquid crystal display device with the pattern of the black matrix as a mask prevents the exposing of the wiring.
In addition, forming an ultraviolet light-blocking layer on the thin film transistor substrate prevents the degradation of the properties of the substrate. Thus, it becomes possible to prevent an increase in the number of processes because the black matrix serves as the ultraviolet light-blocking layer.
Further, because the protective films formed above and below the black matrix serve as spacers, the process of scattering spacers can be omitted, which increases throughput and reduces cost.
Also, by forming the pattern doubling as spacers only in the direction of the source lines, injection of the liquid crystal becomes easy. In this case, since the gate lines or the capacitance lines serve as the black matrix in the direction of the gate lines, it is no longer necessary to separately form a black matrix in the direction of the gate lines, and thus respective increases of cost avoided. Also, since the liquid crystal injection port is formed in the direction of the source lines, injection of the liquid crystal can be performed in an even shorter time and with good yield.
Further, by forming the pattern doubling as spacers only in the direction of the gate lines, the gate lines or the capacitance lines serve as the black matrix in the direction of the source lines. Therefore, it is no longer necessary to separately form a black matrix in the direction of the source lines. Also, since the liquid crystal injection port is formed in the direction of the gate lines, injection of the liquid crystal can be performed in an even shorter time and with good yield.
In addition, by separating the anti-static wiring formed on the lower part of the liquid crystal display device using the pattern from the black matrix or protective film or the pattern of the contact hole as a mask, it becomes possible to reduce the number of processes and the cost.
Other objects, advantages and salient features of the invention will become apparent to one skilled in the art from reading the detailed description taken in conjunction with the annexed drawings which disclose preferred embodiments.